[Removal Mechanism of Microplastics in Bioretention Systems and the Influence of Their Enrichment on the Treatment of Pollutants in the System].

Stormwater washes microplastics deposited on road dust or floating in the air into urban pipeline networks and then into rivers， lakes， and oceans， which is a direct threat to ecosystems and human health. Therefore， there is an urgent need to implement control measures for microplastics in runoff. As one of the low-impact development strategies， bioretention systems can remove various pollutants， including microplastics， from runoff through natural processes such as adsorption and filtration by soil media， absorption by plants， and biodegradation by microorganisms， demonstrating effective microplastic management. However， due to their large specific surface area and resistance to degradation， most microplastics tend to accumulate within these systems， easily forming composite pollution with other contaminants， which hinders the removal of nutrients by bioretention systems. Based on a comprehensive analysis of domestic and international research on bioretention systems， this study summarizes the microplastic removal processes within bioretention systems and further explores the impact of microplastic accumulation on the nutrient treatment capabilities of these systems. The results indicated that microplastic accumulation altered the physicochemical properties of the soil media in bioretention systems， impeded plant growth and development， and inhibited the abundance and activity of relevant enzymes and microorganisms involved in nutrient processing. Notably， the removal of dissolved nitrogen， which primarily occurs through biodegradation processes in these systems， was significantly affected. The findings of this study provide scientific insights for microplastic management and the optimization of bioretention system performance. It also highlights future research directions， including the microplastic removal method， microplastic ageing mechanism， system numerical simulation， and so on.